Rendering specific colors from color printing systems can vary over time, and sometimes within a single job. In addition, environmental conditions, such as humidity and temperature, greatly affect toner and a particular system's print capabilities. The degree to which a particular color can vary and still be acceptable can differ based on a number of factors, such as, for example, the requirements of the customer, the specific job being printed, the print shop handling the print job, the specific color being printed, etc. Print shops that require a high degree of color fidelity typically inspect the printed job output at some specified interval. These inspections are often visual, but may also include offline measurement devices. This can be a time-sensitive and costly process.
U.S. Pat. No. 6,175,700, herein incorporated by reference in its entirety, describes a method for printing test patterns that are interleaved in large print jobs. The disclosed method enables periodic sampling of colors while a job is printing, allowing the customer to monitor color quality during production. However, the customer must visually review (with the naked-eye) the printed sample test patterns, and stop the printing process to take remedial action, if necessary.
Some printing systems use inline measurements device, but these typically rely on color patterns that are trimmed from (or hidden from) the final customer document, such as on a photoreceptor belt, and therefore are not well-suited to document printers.